The NFL rates its passers for statistical purposes against a fixed performance standard based on statistical achievements of all qualified pro passers since 1960.

The current system, which was adopted in 1973, removes inequities that existed in the former method and, at the same time, provides a means of comparing passing performances from one season to the next.

It is important to remember that the system is used to rate passers, not quarterbacks. Statistics do not reflect running ability, leadership, play-calling, and other intangible factors that go into making a successful professional quarterback.